Interaction between competitors and predators and its effects on morphological and behavioural defences in Scinax nasicus tadpoles

Abstract

Predation affect the behaviour of organisms, and the number of conspecifics can influence the perception of predation risk. Two main types of traits, morphological and behavioural, are involved in the induced defences of many organisms. Here, we examined the influence of chemical cues of the predators Belostoma elongatum (Hemiptera, Belostomatidae) and Moenkhausia dichroura (Characiformes, Characidae) on the morphology, growth, development and activity of Scinax nasicus larvae. Our main goal was to determine whether the investment in morphological or behavioural defences varied according to the number of conspecifics and to the chemical cues of predators. To this end, we performed two experiments under microcosm conditions. In experiment 1, we determined morphological defences in tadpoles by analyzing changes in morphology, growth rate and development rate, whereas in experiment 2, we determined behavioural defences by analyzing changes in the activity of tadpoles. The experimental design consisted of two tadpole densities, with and without chemical cues of predators. We found that: 1) larval morphology, growth and development were significantly affected by density; 2) the chemical cues of the predators did not influence the morphology, growth or development of tadpoles; 3) tadpoles at high densities were more active than those at low densities; 4) tadpoles decreased the activity in the presence of chemical cues of M. dichroura; and 5) tadpoles increased the activity in the presence of chemical cues of B. elongatum. Our results suggest that density is a determinant factor of tadpole morphology of and that Scinax nasicus larvae respond to predators with behavioural defences, which vary according to the type of predator.